The MA−4: SPP1+ FABP5+ intermediate class likely arose from bone marrow-derived macrophages60 with its high accessibility and expression for SPP1 (Fig. 4b); bone marrow-derived macrophages are known be abundant in active RA and induce proinflammatory cytokines/chemokines13,61. The gene discussed is FABP5; the disease is rheumatoid arthritis.